55 V8 Differential code - What's yours?

[Troy P.]

I have an early (#78) 55 V8 with a MW differential made in May (presumably 1954). Number 29 also has a MW made in May. Book says both should be AE coded.

I have a theory that, just like the frames, side curtains and tan tops, left over 54 MW differentials were used in at least early 55 and maybe well into the model year. If you have a 55 please let me know what differential code you have and your car number.

A previous 53-55 team leader and 55 restorer told me he had never seen an AE rear. But I believe they exist as I've seen photos of two...assuming they have not been changed to meet judging expectations. Nevertheless his experience may be telling us that MW differentials were prevalent in 55.

I have another theory about the differential codes.

We understand the stamped numbers are the month and day of assembly. But its very odd that there is no year in the date code. The other thing that is odd is LW, MW, and AE rears seem to be identical - same gears, same bearings, same seals, same gaskets. So if they are the same why do they have a different letter code? My theory is the letter code tells us the year of manufacture and not necessarily the year of installation in a car.

[John S.]

Re: 55 V8 Differential code - What's yours?

AE 9 06 is the original differential on my car.

[Troy P.]

Re: 55 V8 Differential code - What's yours?

What car number is that, John?

[Troy P.]

Re: 55 V8 Differential code - What's yours?

I'm disappointed with the attempt to survey owners through this forum. Only one persons replied. However, through research and calling/emailing other 55 owners I did find some answers.

As you know the letter codes for 53-55 differentials are supposed to be LW, MW and AE. The numbers that follow are the month and date of assembly - no year specified. So that lead me to strongly suspect the letter code was the year. I was correct.

I found a Technical Service Bulletin written in 53 that shows L was the code for differentials having been made in the 1953 model year and the following letter W was the plant at which the part was assembled. So an LW rear was assembled in model year 1953. That does not mean that all 53s came with a LW differentials and it does not mean that some early 54s could come not with a LW.

Knowing that L means assembled in model year 53 leads me to conclude that M means model year 54 and A means model year 55.

My survey of early 55 owners turned up three original examples of having MW differentials and two with 54 rear springs. (Probably 54 shocks too, but I did not check.) The three cars with MWs are #29, #63 and #78. I'm still trying to get info on #7. (If anyone has an early 55 please jump in with your data.)

The interesting thing is all three of the early 55s with MWs have May 1954 date codes. Two of the three had original springs and they have May 54 date codes. So it appears a surplus of differentials and springs built up in May when Chevy expected to sell more 54s than proved to be the case.

We know that a lot of left over parts from 54 were used in 55; dated parts such as seats, gauges, side curtains and tops. I believe we can now add differentials and rear springs. Similarly we know left over 53 parts were used in early 54.

The 56-57 NCRS TIMJG advises readers and judges that they will find a mix of 55 parts on early 56's and some 57 parts on late 56s. Perhaps the 53-55 TIMJG should contain a similar warning about crossovers.

Additional survey would be required to determine when they ran out of MW differentials and AE's started to appear. Anyone interested in that task?

[John S.]

Re: 55 V8 Differential code - What's yours?

I'm disappointed with the attempt to survey owners through this forum. Only one persons replied. However, through research and calling/emailing other 55 owners I did find some answers.

As you know the letter codes for 53-55 differentials are supposed to be LW, MW and AE. The numbers that follow are the month and date of assembly - no year specified. So that lead me to strongly suspect the letter code was the year. I was correct.

I found a Technical Service Bulletin written in 53 that shows L was the code for differentials having been made in the 1953 model year and the following letter W was the plant at which the part was assembled. So an LW rear was assembled in model year 1953. That does not mean that all 53s came with a LW differentials and it does not mean that some early 54s could come not with a LW.

Knowing that L means assembled in model year 53 leads me to conclude that M means model year 54 and A means model year 55.

My survey of early 55 owners turned up three original examples of having MW differentials and two with 54 rear springs. (Probably 54 shocks too, but I did not check.) The three cars with MWs are #29, #63 and #78. I'm still trying to get info on #7. (If anyone has an early 55 please jump in with your data.)

The interesting thing is all three of the early 55s with MWs have May 1954 date codes. Two of the three had original springs and they have May 54 date codes. So it appears a surplus of differentials and springs built up in May when Chevy expected to sell more 54s than proved to be the case.

We know that a lot of left over parts from 54 were used in 55; dated parts such as seats, gauges, side curtains and tops. I believe we can now add differentials and rear springs. Similarly we know left over 53 parts were used in early 54.

The 56-57 NCRS TIMJG advises readers and judges that they will find a mix of 55 parts on early 56's and some 57 parts on late 56s. Perhaps the 53-55 TIMJG should contain a similar warning about crossovers.

Additional survey would be required to determine when they ran out of MW differentials and AE's started to appear. Anyone interested in that task?

It seems to me anything you get from #78 would be questionable. Info I have on it is a red car with a 3-speed, which neither show any originality. Other items under cars that you might address is the transition date of the 188 to 243 torque converter and when 55 dated shocks might appear

[Benjamin C.]

Re: 55 V8 Differential code - What's yours?

Hi Troy. I own car #300 built on May 31,1955. My rear end code is MW 3 25.

[David B.]

Re: 55 V8 Differential code - What's yours?

Your rear axle research appears to be on track for 1953 & 54. However you might want to look a little further before stating the stamped axle letter "A" indicates the year 1955.
In 1955 GM changed the axle ID designation into: 1955 (1st series) & 1955 (2nd series). Thereafter the prefix "A"" identified the G & A assembly plant in Detroit and "B" identified Buffalo G & A as the assembly plant.

[Troy P.]

Re: 55 V8 Differential code - What's yours?

Thank you for your input David. My research indicated the second letter was the plant, presumably one of the two plants you identified. However, neither of the two published plant codes in 53 were a "W". Not sure what that means but it might indicate Corvette differentials were assembled somewhere other than the two primary rear end plants. Following that could tell us that in 55 Corvette rears were not assembled or at least not stamped with the code for either of those two main plants.

I'm confident the first letter is the year and the second is the plant. I just can't say what plant W or E indicate. Still very open to more news on that subject if anyone has access to GM documents.

I also found they seemed to randomly pick letters each year for the year code and plant. Not sure why they didn't use the same code for Detroit and Buffalo every year. So the W plant in 53-54 may well be the same plant as E in 55...which would make sense.

As you know the 53-55 differential is almost the same as the 49-54 passenger car. Passenger car was set up to attach to a torque tube whereas Corvette was modified for a Hotchkiss type open drive shaft. I'm almost 100% confident I've read that the passenger car rear did not stand up to the increased 150, 155, or 195 horsepower of the Corvette engines and the gears in the Corvette differential gears are heat treated to give them greater strength/durability. Otherwise they share the same bearings, seals (except pinion) and gaskets. Perhaps the Detroit and Buffalo plants did not have heat treat capability and the Corvette differentials were sent elsewhere for heat treat and final assembly. If so that would explain why they do not carry a Detroit or Buffalo plant assembly code.

[Troy P.]

Re: 55 V8 Differential code - What's yours?

As we discussed the red #78 you were thinking of was likely #378 or #478 or #578.


As you indicated, there are lots of parts transition dates that could be researched. Off the top of my head another is when did Hallett MFG. tags stop showing up on the ignition shielding.

Additional research is just a matter of finding volunteers willing to undertake that work. Volunteers are very scarce. Thus Steve Newsom and I spent literally months of our time on the last edition of the 53-55 TIMJG and it looks like I'm starting that amount of effort again. Meanwhile if you have suggested corrections or additional research information to input please contact Team Leader Greg Piccone.

[David B.]

Re: 55 V8 Differential code - What's yours?

Troy, I must admit I am a little puzzled where you are doing your "research". I thought differential info for all Corvettes have been explained in detail long ago. Perhaps I am assuming too much. If you give me your email I will forward all the info you are looking for.
P.S. W is Corvette powerglide for 53 & 54 built at G & A (not Buffalo)

[Troy P.]

Re: 55 V8 Differential code - What's yours?

I'm very interested in anything you have to share. My email is troy.pyles@comcast.net

TSB #276 issued July 7, 1953 lists all the rear axels by ratio, their model year code and plant. None of the plant codes include W. Practically every other letter in the alphabet was listed though - actually 28 letters used for coding of either Gear & Axel or Buffalo, depending on the ratio. But this bulletin came out about the time of initial Corvette production and did not list the 3.55:1 axel.

There is another TSB #249 that also has rear axel codes but I don't have that one. But it was issued even earlier and I doubt it would include Corvette.

1953 Corvette serial, engine and rear axel numbers are explained in The Product Data Book published by the Service and Mechanical Department. In a section dated 10-2-53 it shows the Corvette rear axel to have a Model L and a Plant (Gear & Axel) W.

Following that trend I surmised MW is a model year 54 axel assembled possibly at G&A (if the plant letter code did not change from year to year)and AE is a 55 model year assembled at some location not known to me. Hopefully your data will show what plant E is.

One difference between those two cited documents is one refers to the first letter as the "model year" and the other just "model". Nevertheless I believe the letter code to be equivalent to a year code. Otherwise 53 and 54 rear axels would both be L as the model is the same - just not the year.

[Troy P.]

Re: 55 V8 Differential code - What's yours?

Refocusing for a second, the intent of my research is to affirm or deny that left over MW rear axels were used in early 55. So far three early cars have been observed with May dated MWs and one somewhat later production 55 with a March MW. Hopefully the documents you have to share will shed some light on this.

The question of what plant is represented by the W and E is a side interest issue.

[Troy P.]

Re: 55 V8 Differential code - What's yours?

Just received photos of unrestored 55 #217 (Harvest Gold). Photo shows it has rear axel code MW 5 24. This is the 4th confirmed MW in a 55 with a May date. As reported above by BJ, the 5th example #300 has a March date.

Now I think it safe to say my theory that early 55s came with left over MW rears is true.

Anyone else have an example to share - early or late?

[David B.]

Re: 55 V8 Differential code - What's yours?

Email sent, hope it clears up any questions.

[Troy P.]

Re: 55 V8 Differential code - What's yours?

The information provided indicates L was built in model year 53 and M was built in model year 54. Interestingly they dropped the year code in 55 and the AE just indicates what plant the rear axel was built.

Once again the information tells us when the rears were built but does not tell us when they were installed. As previously reported, I think it clear from my survey data that MW continued to be installed in 55. I would also suggest that some early 54s may be found with LW as I doubt exactly 300 LWs were built. Any volunteers to take up that research?

The data David provided also says that 55 3 speed Corvettes should have an AD rear end (TIMJG say AE). I will look into that a bit as my effort is oriented in getting the 53-55 TIMJG correct. But need a volunteer to continue researching 55 rears to determine approximately when the MW install ended and AEs began.